1. Field of the Invention
The invention concerns combustion chambers of the type used mainly in aviation turbojets, which are intended for ensuring the combustion of a fuel in a high-pressure air flow. These chambers consist of a wall, called the flame tube, arranged lengthwise in the air flow and provided with a cooling device which includes measures for forming a film of air on the internal surface of the wall so as to protect it from the direct action of the flame. This cooling procedure is known under the name of "film cooling."
The major problem posed by this procedure is that of sufficiently slowing down the cooling air to a desired velocity equal to the speed of the hot gasses, thereby enabling the cooling air to flow along the internal surface of the wall to be cooled while forming a uniform film over it.
2. Description of the Prior Art
It has previously been proposed to have the air enter through a number of small holes made in a part of the wall to be cooled which is flared in shape; it is thought that in this way there will be rapid slackening in the speed of the small streams of air passing through the holes.
Moreover, it is known that the permeability of a surface perforated in many places is slight.
It has also been proposed to add, to the combustion chamber tube flame wall, annular shoulders which make up sorts of annular pockets, regularly spaced longitudinally and separated from the interior of the flame tube by a portion of the wall or a small tongue which is oriented axially, and to introduce the cooling air in these pockets, from which it comes out in an axial direction across the slot which exists between the small tongue and the flame tube. But, in this earlier proposal, the holes being used as air intakes in each of these pockets were not numerous and were relatively large in diameter, so that within the pockets the slackening of speed was not carried out properly unless a small tongue with a substantial axial length was provided, which constitutes a problem because the small tongue, in that it is exposed to extreme thermal constraints, threatens to become disfigured in a manner prejudicial to the effectiveness of the air film.
In order to shorten the small tongue, it has of course been proposed to provide intake orifices in the pocket is such a way that the flow of cold air must be reversed before it leaves the pocket, or even to provide a baffle in the pocket. These solutions give rise to problems, however, by creating harmful turbulence.